Motor cortex

Question 1

Describe the difference between decerebrate and decorticate rigidity?

Answer 1

Decerebrate: extension of upper and lower limbs

Decorticate: extension of lower limbs, but flexion of upper limbs

Question 2

What do cecerebrate and decorticate rigidity result from?

Answer 2

Loss of brain control over spinal cord

Question 3

In which pathway is the red nucleus found?

What is its function?

Where does it project to?

Answer 3

Lateral corticospinal tract

Initiates flexion in distal musculature

Projects to rubrospinal tract

Question 4

Contrast the location of the reticular formation and the red nucleus?

Answer 4

Reticular formation: pons and medulla

Red nucleus: midbrain

Question 5

Describe the inputs to the reticular formation and the red nucleus?

What is the consequence of this?

Answer 5

A lot of drive from cortical inputs, most of which is inhibitory

So, there is tonic inhibitory control over these nuclei, ongoing suppression

Question 6

What happens when inhibitory control over the reticular formation and red nuclei are lost?

Explain.

Answer 6

Depends on location of lesion

Removal of cortical input to all levels of brainstem > decoritcate rigidity (free running reticular formation > extensors dominant, free running red nucelus > flexion wins out over extensors in arms)

Level of disruption below midbrain > decerebrate rigidity (still disinhibition of reticular formation > extensors dominate)

Question 7

What does progression from decorticate to decerebrate rigidity signify?

Answer 7

There is a lesion that is progressing to include more and more of the brainstem

Question 8

Describe Babinski’s sign?

Answer 8

Upgoing plantar reflex (dorsiflexion) and fanning toes

Question 9

What is Babinski’s sign indicative of?

Answer 9

Loss of brain control over spinal cord

Descending tract damage

Question 10

When is Babinski’s sign normal?

Why?

Answer 10

In first 12-24 months of life

Brain hasn’t yet developed functional control over spinal cord

DF seems like a sensible response when crawling

Question 11

Why are monosynpatic reflexes so informative?

Answer 11

Final commmon pathway

Tell us about how the motor neurons are working in the context of everything above them

Part of an hierarchy

Question 12

What is the general approach to identifying UMN lesions in cranial nerves?

Answer 12

Pattern of loss (rather than UMN/LMN signs seen with spinal motor input)

Question 13

What is the upper motor neuron input to the cranial nerves called?

Answer 13

Corticobulbar innervation

Question 14

Describe the pattern of corticobulbar innervation to the cranial nerves?

Answer 14

Bilateral innervation, except to lower face and tongue (contralateral innervation only)

Face: one nucleus for upper, one nucleus for lower

Question 15

How can upper and lower motor neuron lesions to the facial nerve be identified?

Explain.

Answer 15

Lower motor neuron lesion: both upper and lower facial nuclei affected > weakness of superior and inferior facial muscles

Upper motor neuron lesion: bilateral innervation to upper face > upper face unaffected

However, lower face only receives contraletral innervation > weakness of inferior contralateral facial muscles

Question 16

What is the beneift of EMG?

Answer 16

High temporal resolution

Very helpful in telling us when a muscle is active or inactive

Question 17

What are the two components to most motor control?

Answer 17

Anticipation: knowledge of task and preparing for action

Reflex control: negative feedback control of muscle position

Question 18

Describe the integration between anticipation and reflex control that occurs during the task of catching a ball?

Answer 18

Question 19

Describe the anticipatory involuntary movements involved in lifting one leg laterally?

Answer 19

Question 20

Describe the anatomy behind the control of the anticipatory involuntary movements?

Answer 20

Direct cortical pathway that is ipsilateral and joins up with ventral pathways

Question 21

How do we know that locomotion is controlled by the lumbosacral spinal cord?

Answer 21

Newborn babies and anencephalics exhibit locomotor reflex

At this stage, brain does not have control over spinal cord

Question 22

Describe the phases of locomotion?

Answer 22

Stance phase: associated with weight bearing, so extensors active, move into flexion at the end

Swing phase: associated with movement, so flexors active, with a bit of extension for grounding at the end

Question 23

How do decerebrate cats increase speed of locomotion when treadmill speed is increased?

Answer 23

Sesnory information is coming from the limbs

Information from muscle spindle and Golgi tendon organs

Input from periphery to tell you which stage of the locomotion cycle you are in, and what you need to do next

Question 24

What controls the initiation of the swing phase in locomtion?

Answer 24

Sensory feedback from extensor muscles

Question 25

Why is cortical input required for locomotion, if the pattern generator is located in the spinal cord?

Answer 25

Motor cortex responsible for sending information down to pattern generator to chnage pattern when we have to do something out of the ordinary

Question 26

List some of the abnormal gait patterns associated with CNS disorders?

Answer 26

Ataxic gait

Choreaform gait

Hemiparetic gait

Circumducting gait

Parkinsonian gait